Internet Engineering Task Force (IETF) W. Dec, Ed.
Request for Comments: 6911 Cisco Systems, Inc.
Category: Standards Track B. Sarikaya
ISSN: 2070-1721 Huawei USA
G. Zorn, Ed.
Network Zen
D. Miles
Google
B. Lourdelet
Juniper Networks
April 2013
RADIUS Attributes for IPv6 Access Networks
Abstract
This document specifies additional IPv6 RADIUS Attributes useful in
residential broadband network deployments. The Attributes, which are
used for authorization and accounting, enable assignment of a host
IPv6 address and an IPv6 DNS server address via DHCPv6, assignment of
an IPv6 route announced via router advertisement, assignment of a
named IPv6 delegated prefix pool, and assignment of a named IPv6 pool
for host DHCPv6 addressing.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6911.
Dec, et al. Standards Track [Page 1]

RFC 6911 RADIUS IPv6 Access April 20131. Introduction
This document specifies additional RADIUS Attributes used to support
configuration of DHCPv6 and/or ICMPv6 Router Advertisement (RA)
parameters on a per-user basis. The Attributes, which complement
those defined in [RFC3162] and [RFC4818], support the following:
o The assignment of specific IPv6 addresses to hosts via DHCPv6.
o The assignment of an IPv6 DNS server address, via DHCPv6 or Router
Advertisement [RFC6106].
o The configuration of more specific routes to be announced to the
user via the Route Information Option defined in [RFC4191],
Section 2.3.
o The assignment of a named delegated prefix pool for use with "IPv6
Prefix Options for Dynamic Host Configuration Protocol (DHCP)
version 6" [RFC3633].
o The assignment of a named stateful address pool for use with
DHCPv6 stateful address assignment [RFC3315].
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Deployment Scenarios
The extensions in this document are intended to be applicable across
a wide variety of network access scenarios in which RADIUS is
involved. One such typical network scenario is illustrated in Figure
1. It is composed of an IP Routing Residential Gateway (RG) or host;
a Layer 2 Access Node (AN), e.g., a Digital Subscriber Line Access
Multiplexer (DSLAM); an IP Network Access Server (NAS) (incorporating
an Authentication, Authorization, and Accounting (AAA) client); and a
AAA server.
Dec, et al. Standards Track [Page 3]

RFC 6911 RADIUS IPv6 Access April 2013
+-----+
| AAA |
| |
+--+--+
^
.
.(RADIUS)
.
v
+------+ +---+---+
+------+ | | | |
| RG/ +-------| AN +-----------+----------+ NAS |
| host | | | | |
+------+ (DSL) +------+ (Ethernet) +-------+
Figure 1
In the depicted scenario, the NAS may utilize an IP address
configuration protocol (e.g., DHCPv6) to handle address assignment to
RGs/hosts. The RADIUS server authenticates each RG/host and returns
the Attributes used for authorization and accounting. These
Attributes can include a host's IPv6 address, a DNS server address,
and a set of IPv6 routes to be advertised via any suitable protocol,
e.g., ICMPv6 (Neighbor Discovery). The name of a prefix pool to be
used for DHCPv6 Prefix Delegation or the name of an address pool to
be used for DHCPv6 address assignment can also be Attributes provided
to the NAS by the RADIUS AAA server.
The following subsections discuss how these Attributes are used in
more detail.
2.1. IPv6 Address Assignment
DHCPv6 [RFC3315] provides a mechanism to assign one or more non-
temporary IPv6 addresses to hosts. To provide a DHCPv6 server
residing on a NAS with one or more IPv6 addresses to be assigned,
this document specifies the Framed-IPv6-Address Attribute
(Section 3.1).
While [RFC3162] permits the specification of an IPv6 address via the
combination of the Framed-Interface-Id and Framed-IPv6-Prefix
Attributes, this separation is more natural for use with PPP's IPv6
Control Protocol than it is for use with DHCPv6, and the use of a
single IPv6 address Attribute makes for easier processing of
accounting records.
Dec, et al. Standards Track [Page 4]

RFC 6911 RADIUS IPv6 Access April 2013
Because DHCPv6 can be deployed on the same network as ICMPv6
stateless address autoconfiguration (SLAAC) [RFC4862], it is possible
that the NAS will require both stateful and stateless configuration
information. Therefore, it is possible for the Framed-IPv6-Address,
Framed-IPv6-Prefix, and Framed-Interface-Id Attributes [RFC3162] to
be included within the same packet. To avoid ambiguity in this case,
the Framed-IPv6-Address Attribute is intended for authorization and
accounting of DHCPv6-assigned addresses, and the Framed-IPv6-Prefix
and Framed-Interface-Id Attributes are used for authorization and
accounting of addresses assigned via SLAAC.
2.2. DNS Servers
DHCPv6 provides an option for configuring a host with the IPv6
address of a DNS server. The IPv6 address of a DNS server can also
be conveyed to the host using ICMPv6 with Router Advertisements, via
the Recursive DNS Server Option [RFC6106]. To provide the NAS with
the IPv6 address of one or more DNS servers, this document specifies
the DNS-Server-IPv6-Address Attribute (Section 3.2).
2.3. IPv6 Route Information
The IPv6 Route Information Option [RFC4191], is intended to be used
to inform a host connected to the NAS that a specific route is
reachable via any given NAS.
This document specifies the Route-IPv6-Information Attribute
(Section 3.3) that allows the AAA server to provision the
announcement by the NAS of a specific Route Information Option to an
accessing host. The NAS may advertise this route using the method
defined in RFC 4191 or other equivalent methods. Any other
information, such as preference or lifetime values, that is to be
present in the actual announcement using a given method is assumed to
be determined by the NAS using means not specified by this document
(e.g., local configuration on the NAS).
While the Framed-IPv6-Prefix Attribute ([RFC3162], Section 2.3)
allows the route to be advertised in an RA, it cannot be used to
configure more specific routes. While the Framed-IPv6-Route
Attribute ([RFC3162], Section 2.5) causes the route to be configured
on the NAS and potentially to be announced via an IP routing
protocol, depending on the value of Framed-Routing, it does not
result in the route being announced in an RA.
Dec, et al. Standards Track [Page 5]

RFC 6911 RADIUS IPv6 Access April 20132.4. Delegated IPv6 Prefix Pool
DHCPv6 Prefix Delegation (DHCPv6-PD) [RFC3633] involves a delegating
router selecting a prefix and delegating it on a temporary basis to a
requesting router. The delegating router may implement a number of
strategies as to how it chooses what prefix is to be delegated to a
requesting router, one of them being the use of a local named prefix
pool. The Delegated-IPv6-Prefix-Pool Attribute (Section 3.4) allows
the RADIUS server to convey a prefix pool name to a NAS that is
hosting a DHCPv6-PD server and that is acting as a delegating router.
Because DHCPv6 Prefix Delegation can be used with SLAAC on the same
network, it is possible for the Delegated-IPv6-Prefix-Pool and
Framed-IPv6-Pool Attributes to be included within the same packet.
To avoid ambiguity in this scenario, use of the Delegated-IPv6-
Prefix-Pool Attribute should be restricted to authorization and
accounting of prefix pools used in DHCPv6 Prefix Delegation, and the
Framed-IPv6-Pool Attribute should be used for authorization and
accounting of prefix pools used in SLAAC.
2.5. Stateful IPv6 Address Pool
DHCPv6 [RFC3315] provides a mechanism to assign one or more non-
temporary IPv6 addresses to hosts. Section 3.1 introduces the
Framed-IPv6-Address Attribute to be used to provide a DHCPv6 server
residing on a NAS with one or more IPv6 addresses to be assigned to
the clients. An alternative way to achieve a similar result is for
the NAS to select the IPv6 address to be assigned from an address
pool configured for this purpose on the NAS. This document specifies
the Stateful-IPv6-Address-Pool Attribute (Section 3.5) to allow the
RADIUS server to convey a pool name to be used for such stateful
DHCPv6-based addressing and for any subsequent accounting.
3. Attributes
The fields shown in the diagrams below are transmitted from left to
right.
3.1. Framed-IPv6-Address
The Framed-IPv6-Address Attribute indicates an IPv6 address that is
assigned to the NAS-facing interface of the RG/host. It MAY be used
in Access-Accept packets and MAY appear multiple times. It MAY be
used in an Access-Request packet as a hint by the NAS to the RADIUS
server that it would prefer this IPv6 address, but the RADIUS server
is not required to honor the hint. Because it is assumed that the
Dec, et al. Standards Track [Page 6]

RFC 6911 RADIUS IPv6 Access April 20133.2. DNS-Server-IPv6-Address
The DNS-Server-IPv6-Address Attribute contains the IPv6 address of a
DNS server. This Attribute MAY be included multiple times in Access-
Accept packets when the intention is for a NAS to announce more than
one DNS server address to an RG/host. The Attribute MAY be used in
an Access-Request packet as a hint by the NAS to the RADIUS server
regarding the DNS IPv6 address, but the RADIUS server is not required
to honor the hint.
The content of this Attribute can be copied to an instance of the
DHCPv6 DNS Recursive Name Server Option [RFC3646] or to an IPv6
Router Advertisement Recursive DNS Server Option [RFC6106]. If more
than one DNS-Server-IPv6-Address Attribute is present in the Access-
Accept packet, the addresses from the Attributes SHOULD be copied in
the same order as received.
A summary of the DNS-Server-IPv6-Address Attribute format is given
below. The format of the Address field is the same as that of the
corresponding field in the NAS-IPv6-Address Attribute [RFC3162].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address (cont)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Address (cont) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
169 for DNS-Server-IPv6-Address
Length
18
Address
The 128-bit IPv6 address of a DNS server.
Dec, et al. Standards Track [Page 8]

RFC 6911 RADIUS IPv6 Access April 20133.3. Route-IPv6-Information
The Route-IPv6-Information Attribute specifies a prefix (and
corresponding route) for the user on the NAS, which is to be
announced using the Route Information Option defined in "Default
Router Preferences and More Specific Routes" [RFC4191], Section 2.3.
It is used in the Access-Accept packet and can appear multiple times.
It MAY be used in an Access-Request packet as a hint by the NAS to
the RADIUS server, but the RADIUS server is not required to honor the
hint. The Route-IPv6-Information Attribute format is depicted below.
The format of the prefix is as per [RFC3162].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved | Prefix-Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Prefix (variable) .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
170 for Route-IPv6-Information
Length
Length, in bytes. At least 4 and no larger than 20; typically, 12
or less.
Prefix Length
8-bit unsigned integer. The number of leading bits in the prefix
that are valid. The value can range from 0 to 128. The prefix
field is 0, 8, or 16 octets depending on Length.
Prefix
Variable-length field containing an IP prefix. The prefix length
field contains the number of valid leading bits in the prefix.
The bits in the prefix after the prefix length, if any, are
reserved and MUST be initialized to zero.
Dec, et al. Standards Track [Page 9]

RFC 6911 RADIUS IPv6 Access April 20133.4. Delegated-IPv6-Prefix-Pool
The Delegated-IPv6-Prefix-Pool Attribute contains the name of an
assigned pool that SHOULD be used to select an IPv6 delegated prefix
for the user on the NAS. If a NAS does not support prefix pools, the
NAS MUST ignore this Attribute. It MAY be used in an Access-Request
packet as a hint by the NAS to the RADIUS server regarding the pool,
but the RADIUS server is not required to honor the hint.
A summary of the Delegated-IPv6-Prefix-Pool Attribute format is shown
below.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
171 for Delegated-IPv6-Prefix-Pool
Length
Length, in bytes. At least 3.
String
The string field contains the name of an assigned IPv6 prefix pool
configured on the NAS. The field is not NULL (hexadecimal 00)
terminated.
Note: The string data type is as documented in [RFC6158] and carries
binary data that is external to the RADIUS protocol, e.g., the name
of a pool of prefixes configured on the NAS.
Dec, et al. Standards Track [Page 10]

RFC 6911 RADIUS IPv6 Access April 20133.5. Stateful-IPv6-Address-Pool
The Stateful-IPv6-Address-Pool Attribute contains the name of an
assigned pool that SHOULD be used to select an IPv6 address for the
user on the NAS. If a NAS does not support address pools, the NAS
MUST ignore this Attribute. A summary of the Stateful-IPv6-Address-
Pool Attribute format is shown below. It MAY be used in an Access-
Request packet as a hint by the NAS to the RADIUS server regarding
the pool, but the RADIUS server is not required to honor the hint.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
172 for Stateful-IPv6-Address-Pool
Length
Length, in bytes. At least 3.
String
The string field contains the name of an assigned IPv6 stateful
address pool configured on the NAS. The field is not NULL
(hexadecimal 00) terminated.
Note: The string data type is as documented in [RFC6158] and carries
binary data that is external to the RADIUS protocol, e.g., the name
of a pool of addresses configured on the NAS.
3.6. Table of Attributes
The following table provides a guide to which Attributes may be found
in which kinds of packets, and in what quantity. The optional
inclusion of the options in Access Request messages is intended to
allow for a NAS to provide the RADIUS server with a hint of the
Attributes in advance of user authentication, which may be useful in
cases in which a user reconnects or has a static address. The server
is under no obligation to honor such hints.
Dec, et al. Standards Track [Page 11]